This invention relates to ice composite bodies for use in the construction of fixed or floating structures located in or on water. The invention also relates to a process for the construction of such ice composite bodies.
Ice composite bodies can be used in warm or cool waters for applications such as bridges, breakwaters, causeways, pontoons, artificial islands, dams, tidal barrages, wave power barrages, harbour walls, wind power farms or aircraft runways.
GB-A 2 071 295 discloses a method of producing a gravity ice platform, made in a floating flexible mould from a spray of ice flakes or chips, which are frozen in solid ice by using supercooled water, cold air or a freezing mixture. The resultant large blocks of ice can be used on their own or a number of the blocks may be joined together to form a desired structure. Because of the large volumes of ice involved these structures will sit stably on the waterbed and are capable of withstanding any forces to which they may be subjected, such as from waves, wind currents or collisions.
A problem with structures of this kind is that the ice will tend to creep when subjected to heavy loading. The method of producing the ice structures will also result in large quantities of dissolved gas and also liquid inclusions being trapped in the ice. This will cause the ice to be unstable under stress.
WO 97/25483 discloses an ice composite body having an inner ice core covered by a protective outer armour layer with means for thermally insulating the ice core therebetween. The ice core is frozen and maintained in the frozen state by means of a system of refrigeration pipes located within the body. The ice composite body provides structures of equal or greater strength than equivalent structures using conventional materials, at a significantly lower cost. However, the strength of the ice composite body is limited by the structure of the outer armour shell. A load acting at a point on the upper surface of the armour shell will tend to cause the surface to bend causing stress in the body.
It is an object of the present invention to provide an ice composite body in which the above cited disadvantages are reduced or eliminated. It is also an object of the present invention to provide a process for the construction of an ice composite body, which will produce an ice composite body having predictable load bearing characteristics.
Thus, according to the present invention there is provided an ice composite body for use in the construction of fixed or floating structures located in or on water, the body comprising an inner ice constrained core, a protective outer armour shell having side sections and a separate top section, the top section resting freely between the side sections on the ice core in use and being free to move vertically in use, such that any load acting on the top section will be evenly distributed through the body, means for thermally insulating the ice core and means for maintaining the ice core in a frozen condition in use.
As the inner ice core is constrained within the outer armour shell and as the top section rests on the ice core, the ice core is only stressed in compression. This results in an increase in safe design strength relative to known ice composite bodies.
Preferably, the protective outer armour shell has an inner wall and an outer wall with a space therebetween, the space providing the means for thermally insulating the ice core.
Further, preferably, the space is filled with foam insulating material.
The space between the walls provides a degree of insulation on its own but may also be filled with insulating material.
In certain embodiments, strengthening ribs are located at intervals between the inner and outer walls.
The orientation of the strengthening ribs can be chosen depending on the particular application for which the ice composite body is to be used. Thus, where the application is for a road bridge or aircraft runway the strengthening ribs can be orientated along the length of the bridge or runway so as to be located under the wheel track of the vehicles in use, with suitable lateral stiffeners placed between the ribs.
Preferably, the protective outer armour shell has a base section, side sections, and the top section is located between the side sections and is free to move therebetween.
Thus, the top section rests freely on the ice core in use and is free to move in a vertical direction between the side sections while being retained therebetween. The side sections do not bear any of the weight of the top section.
Further, preferably, one of the side sections further comprises a separate closure section removably located on the upper edge thereof, the closure section being located on the side section in use once the top section is in position.
The removable closure section facilitates the construction of the ice composite body. Thus, the top section can be positioned on the inner ice core with the closure section being put in place on the upper edge of the side section thereafter. The top section is then retained between the two side sections.
Suitably, the space between the top section and the side sections contains a filler material, which prevents any of the core ice from entering the space in use.
The filler provides lateral support and also ensures that the top section always exerts its weight vertically on the ice core top.
Preferably, the filler material is an elastomer or an elastomer-modified bitumen.
To ensure that the top section will always exert its weight vertically on the ice core, the filler material should be chosen from materials such as an elastomer or elastomer-modified bitumen with slightly higher strain in shear at the operating conditions of the ice composite body than the compression strain of the ice under the top section loading and having good adhesion to the armour material chosen.
The filler material is also chosen with reference to the width and vertical dimension of the space between the top section and the side sections, so that the adhesion of the filler to and yield shear stress along the armour used, multiplied by the vertical dimension of the space, is greater than the normal compressive loading on the ice in use.
Further, preferably, a stuffing gasket is located at the upper end of the space between the top section and the side sections to limit the loss of filler therefrom.
In use, the stuffing gasket will be depressed into the space by applied pressure or surface traffic pressure, in order to minimise the expression rate of the filler.
Suitably, the ice composite body is provided with means for replacing any filler lost from the space.
Thus, replacement filler can be pumped into the space at a pressure equal to the compression stress on the top of the ice so as to prevent ice from entering into the space and to ensure that the space is always full of filler.
Preferably, the protective outer armour layer is made of concrete material.
Concrete has been found to be a suitable material for structures constantly immersed in water and provides a life span for the ice composite body of over seventy years when suitably constructed.
Preferably, the inner ice core is formed in layers, each layer having been rolled using a roller apparatus which provides a roller pressure in the range of 3.5 to 8 Newtons/mm2 following formation thereof.
The rolling is carried out in order to orient the strongest axes of the ice crystals of the ice formed in the desired direction. The roller apparatus should exert a compressive pressure above that of the weak ice crystals and below that of the strong ice crystals, typically a roller pressure in the range 3.5-8 Newtons/mm2, with the choice of roller pressure being determined by the particular core strength desired by the designer. This rolling process converts the crystal structure in each ice layer into one with the required mix of strong crystals of known orientation and compressive strength. The rolling of the ice layers in this way also ensures that any average load applied to the top section in use that is below the pressure of the roller used, can be safely withstood by the finished ice core.
Suitably, the means for maintaining the ice core in a frozen condition in use is a plurality of refrigeration pipes passing through the ice core, the refrigeration pipes being connected to a refrigeration unit.
The use of a plurality of refrigeration pipes means that all sections of the inner ice core can be maintained at the desired temperature by suitably distributing the pipes therethrough.
Preferably, the plurality of refrigeration pipes is arranged in parallel groups at various levels throughout the ice core.
Further, preferably, adjacent groups of refrigeration pipes lie at an angle relative to each other.
Advantageously, adjacent groups of refrigeration pipes lie at right angles to each other.
Preferably, a parallel group of refrigeration pipes is located between each layer of ice.
The arrangement of the refrigeration pipes in parallel in groups between each layer of ice with adjacent groups at right angles is an efficient way of controlling the temperature of the ice core and also has advantages as regards the initial formation of the ice core.
Preferably, the plurality of refrigeration pipes includes a set of parallel pipes along the inner wall of each side section.
Having a set of parallel pipes along each wall makes it easier to maintain the ice core at the desired temperature.
In one embodiment the refrigeration unit is located within the space between the inner and outer walls of the protective armour shell.
Placing the refrigeration unit in the space between the inner and outer walls means that the unit can be easily accessed while being protected from the elements.
Preferably, each refrigerant pipe passes through opposing inner walls of the side sections of the protective armour layer and is secured within the space between the inner and outer walls.
By fixing the pipes in this fashion they can add transverse strength to the ice composite body.
Further, preferably, the temperature of individual refrigerant pipes can be controlled independently.
Thus, by controlling the temperature of particular pipes, the temperature of a specific area within the ice core can be altered relative to the surrounding ice.
If a particular area of the interior of the ice composite body needs to be inspected, for example, by a certification authority, after a period of use, the temperature of that area can be adjusted so as to melt the surrounding ice and expose the area to be inspected. Following inspection, the ice composite body can be repaired, if necessary and the area of the core refrozen.
Suitably, an individual refrigerant pipe can be removed from the ice core for repair or replacement.
Thus, an individual pipe can be relined or replaced if needed. This can be achieved by raising the temperature of the pipe so as to free it from the surrounding ice.
In a further embodiment the ice composite body has means for utilising any waste heat generated by the refrigeration unit for heating any buildings located on the ice composite body.
Using the waste heat in this fashion has the advantage not only of providing a cheap source of heat for the buildings but also a profitable method of removing the waste heat from the area of the ice core thus increasing the efficiency of the system.
Suitably, the ice composite body has a backup refrigeration unit.
Different groups of pipes can be usefully connected to primary, secondary or tertiary backup refrigeration systems, powered by different power systems, to increase the level of reliability and security to a level specified by the certification authority, for the use for which the ice composite body is commissioned.
Preferably, the backup refrigeration unit can be used to cool any buildings located on the ice composite body.
Using the backup refrigeration unit in this way makes economic use of the unit which might otherwise remain idle for prolonged periods of time.
Preferably, the ice core is formed from degassed or deionised water.
The use of degassed or deionised water results in the formation of an ice core hang predictable properties.
In a further embodiment the ice composite body further comprises a set of supporting piles, each pile being adapted for fixing to a waterbed at one end thereof, the other end being accommodated in cells constructed within the protective outer shell, the body being free to move in a vertical direction relative to the piles, in response to changing water levels or buoyancy of the body, but not horizontally.
This method of fixing the ice composite body in place means that the piles only need to restrain the body laterally and do not have to support the weight of the body, as it floats in the water.
The ice composite body can also be fixed to the bed using rigid supports fixed to the body. The buoyancy of the ice composite body can be adjusted so that the supports only have to bear a small proportion of the weight of the body.
In both cases the ice composite body is not fixed directly to the water bed and thus the bottom of the body can be inspected if required.
In another aspect, the invention encompasses a process for the construction of an ice composite body as hereinbefore defined comprising the steps of constructing a protective outer armour shell having a base section and side sections, building up an inner ice core within the protective armour shell by successively freezing sufficient amounts of water to form layers of ice, rolling each successive layer of ice with a rolling apparatus to provide a roller pressure in the range of 3.5 to 8 Newtons/mm2, locating a plurality of refrigeration pipes within the body during the ice forming stage, and locating a separate top section of the protective outer armour shell on the top of the completed inner ice core and between the side sections, such that the top section is free to move vertically.
An ice composite body produced in accordance with the above process will contain an inner ice core having a compressive strength of up to 8 Newtons/mm2, with a yield strength for extreme impact loading over short periods of time of 20 Newtons/mm2, an average composite surface bearing strength of up to 8 Newtons/mm2 of surface in total and a local bearing capacity equal to that of the top section used, typically 50 Newtons/mm2 for an armour shell made from concrete material.
Preferably, the protective outer armour layer is constructed in the form of an inner wall and an outer wall with a space therebetween.
An ice composite body having a protective outer armour shell constructed in the form of an inner and outer wall will have an inner ice core, which is only stressed in compression. This will result in an increase in safe design strength up to 8 Newtons/mm2. The physical constraining of the ice along the three orthogonal axes results in ultimate yield strength of the ice of up to 20 Newtons/mm2 for short duration stresses such as in collisions or during a fifty-year wave, thereby increasing the industrial usefulness of ice as an engineering material.
Further, preferably, the space between the inner and outer walls is filled with an insulating material.
Advantageously the filling material is foam insulation.
In one embodiment of the process in accordance with the invention, as each successive amount of water is being frozen to form a layer of ice, the central section of the layer is maintained above freezing point by use of a heating means, and once the remainder of the ice layer has been formed the heating means is removed and the centre portion of the ice layer is frozen.
By using a heating means in this fashion most of the stress due to the lateral expansion of the ice layer is eliminated.
Preferably, the inner surface of the inner wall is coated with a flexible material prior to forming the ice core.
By coating the inner surface of the inner wall with a suitable flexible material any stresses due to the expansion of the central section of the ice layer, following removal of the heating means, can be minimised.
Further, preferably, the flexible material is bitumen.
Suitably, the plurality of refrigeration pipes is arranged in parallel groups at various levels throughout the ice core and adjacent layers of pipes are positioned at an angle relative to each other.
Preferably, the adjacent layers of refrigeration pipes are positioned at right angles to each other.
Further, preferably, a group of refrigeration pipes is located between each layer of ice.
Positioning the refrigeration pipes in this fashion is straightforward and the resulting ice core can be easily maintained in the desired condition.
Suitably, a filler material is added to the space between the top section and the side sections.
Advantageously, a stuffing gasket is located at the upper end of the space between the top section and the side sections.
In a further embodiment of the process in accordance with the invention, the top section is located on top of the inner core by immersing a partially completed body in water and floating the top section into position on the ice core.
Preferably, the top section is floated over a side section of the armour shell, having first removed an upper edge thereof, the upper edge being placed in position once again following correct location of the top section on the ice core.
The step of floating the top section into position allows the top section to be correctly positioned without leaving a gap between the top section and the top of the ice core.
The invention will be further illustrated by the following description of embodiments thereof, given by way of example only with reference to the accompanying drawings.